Ceiling-mounted apparatus for providing a smoke vent or smokeproof screen in the event of a fire

ABSTRACT

An outer frame is fixedly mounted on a ceiling to define a rectangular opening therethrough, which opening is normally closed by a lid having a panel supported by an inner frame so as to be flush with the ceiling. The lid is normally locked in its closed position by means including guides slidable along horizontal grooves formed on the confronting surfaces of the outer frame and by one or more turnable arms connecting the lid to the outer frame, such that when unlocked the lid is caused by gravity to turn to an open position with its free end moving substantially vertically downward as the aforesaid guides coupled to the opposite ends of the lid slide along the horizontal grooves of the outer frame. The apparatus serves either as an emergency smoke vent, in case the outer frame is coupled to a smoke duct, or as a smokeproof screen, in case the outer frame is closed permanently at its upper end.

United States Patent. [1 1 Muramatsu et al.

1 1 CEILING-MOUNTED APPARATUS FOR PROVIDING A SMOKE VENT OR SMOKEPROOF SCREEN IN THE EVENT OF A FIRE [75] Inventors: Mobuhiro Muramatsu; Kosuke Aoki; Masamichi Miki, all of Shizuoka, Japan [73] Assignee: Riken Lightmetal industry Co., Ltd.,

Shizuoka-shi, Shizuoka-ken, Japan [22] Filed: Apr. 10, 1973 [21] Appl. No.: 349,783

[30] Foreign Application Priority Data Apr. 10, 1972 Japan 47-35859 June 6, 1972 Japan 47-66514 June 8, 1972 Japan 47-67775 June 13, 1972 Japan 47-69642 [52] US. Cl 52/1, 49/2, 49/5 [51] Int. Cl E05f 15/20 [58] Field of Search 52/19, 205, 302; 49/154, 49/155, 156, 386, 387, 379; 98/35 [56] References Cited UNITED STATES PATENTS 1,116,767 ll/l9l4 Ullner 49/195 1,380,207 5/1921 Hcgstrom.... 49/7 1,429,967 9/1922 Olshin 52/1 1,716,038 6/1929 Ferris 49/386 1,758,885 5/1930 Clark 49/155 1 Apr. 1,1975

Primary ExaininerErnest R. Purser Assistant Examiner-H. E. Raduazo Attorney, Agent, or FirmBucknam and Archer 7] ABSTRACT An outer frame is fixedly mounted on a ceiling to define a rectangular opening therethrough, which opening is normally closed by a lid having a panel supported by an inner frame so as to be flush with the ceiling. The lid is normally locked in its closed position by means including guides slidable along horizon tal grooves formed on the confronting surfaces of the outer frame and by one or more turnable arms connecting the lid to the outer frame. such that when unlocked the lid is caused by gravity to turn to an open position with its free end moving substantially vertically downward as the aforesaid guides coupled to the opposite ends of the lid slide along the horizontal grooves of the outer frame. The apparatus serves either as an emergency smoke vent, in case the outer frame is coupled to a smoke duct, or as a smokeproof screen, in case the outer frame is closed permanently at its upper end.

4 Claims, 13 Drawing Figures *ATENTEB APR H975 SEiLEI 1 BF 8 FIG.1

AJENTEB APR H975 SHLU 2 0i 8 WATENUB AFR l 1975 SziiEI 3 BF 8 FIG.4

CEILING-MOUNTED APPARATUS FOR PROVIDING A SMOKE VENT ()R SMOKEPROOF SCREEN IN THE EVENT OF A FIRE BACKGROUND OF THE INVENTION This invention relates to apparatus to be mounted on a ceiling for use either as an emergency smoke vent or as a smokeproof screen.

It is a well known fact that various artificially synthesized materials now being used for the construction of buildings can result in the emission of a great deal of smoke and harmful gases in the event of a fire. Even in the early stages of a fire, in which only a narrowly limited portion of the building is actually caught by the flames, the smoke and other combustion gases are known to take a heavy toll of its inhabitants.

This damage can be avoided, at least in part, by the provision of emergency smoke vents communicating the confined spaces of the building with the atmosphere or of smokeproof screens or partitions designed to retard the spread of smoke and other gases.

When a fire breaks out in a room or other enclosed spaces, the smoke first rises to the ceiling, travels along the same. and then starts descending to spread throughout the room. It will accordingly be apparent that the smoke vent or smokeproof screen be provided to the ceiling in order most effectively to exhaust the smoke or to retard its spread throughout the room.

The smoke vent and the smokeproof screen for emergency use can be served by apparatus of substantially the same construction. Conventional versions of such apparatus usually include a frame mounted on a ceiling to define a generally rectangular opening therethrough,

and this opening is normally closed by a turnable lid.

When released, either manually or automatically, the lid is caused by gravity to turn on a fixed fulcrum to the open or vertical position whereby permitting the smoke to escape through the duct in communication with the ceiling opening. Alternatively, the lid itself can serve as the smokeproof screen in its open position if made sufficiently long to span the opposite walls of the room or the like.

However, since the lid turns as aforesaid on the fixed fulcrum in accordance with the prior art, considerable spacings must be provided between the frame and the lid to permit the required motion of the latter. This of course is undesirable from the viewpoint of general appearance of the ceiling. The prior art apparatus has another serious disadvantage in that additional means are required to cushion the impact of the lid rapidly turned to its open position or to prevent the same from swinging to and fro in that open position.

SUMMARY OF THE INVENTION In view of the listed disadvantages of the prior art, it is an object of this invention to provide novel and improved apparatus easily adaptable for use either as an emergency smoke vent or smokeproof screen.

Another object of the invention is to provide appara tus of the character described, in which a lid for normally closing an opening formed through a ceiling by an outer frame is so moved to its open position that the spacings between the lid and the outer frame can be minimized.

Another object of the invention is to provide apparatus of the character described, in which a suitable degrce of friction is imparted to the lid to minimize its impact as the same is moved to its open position.

According to this invention, briefly stated in its perhaps broadest aspects, there is provided apparatus including an outer frame fixedly mounted on a ceiling to define a generally rectangular opening therethrough, the outer frame having horizontally extending guide grooves formed on the confronting inside surfaces thereof. The rectangular opening is provided with a lid which is normally locked in the closed position and which is supported at one end by support means including a plurality of guide portions slidably received in the respective guide grooves of the outer frame. The lid is further connected to the outer frame by at least one turnable arm in such a manner that when unlocked as in the event of a fire, the lid is permitted to move by gravity to the open position while its free end is caused to move substantially vertically downward as the guide portions of the support means travel slidingly along the respective horizontal guide grooves of the outer frame. A smoke duct can be coupled to the outer frame at its upper end so that the smoke produced in the enclosed space under the ceiling will escape therethrough while the lid is in the open position. Alternatively. in case the lid is intended to serve as a smokeproof screen in the open position. the upper end of the outer frame is to be permanently closed.

The features which are believed to be novel and characteristic of this invention are set forth with particularity in the appended claims. The invention itself. however, both as to its construction and mode of operation, together with the further objects and advantages thereof, will be best understood from the following description of preferred embodiments read in connection with the accompanying drawings in which like reference characters denote like parts throughout the several views.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. I is a perspective view of an outer frame for use in the apparatus of this invention;

FIG. 2 is a vertical sectional view of a first preferred embodiment of the invention in which is used the outer frame of FIG. I;

FIG. 3 is a vertical sectional view of the embodiment of FIG. 2 taken along a plane degrees turned from the plane of FIG. 2;

FIG. 4 is a plan view of the embodiment of FIG. 2;

FIG. 5a is a perspective view of an inner frame used in the embodiment of FIG. 2;

FIG. 5b is an enlarged partial sectional view of a modified example of the inner frame of FIG. 5a;

FIG. 5c is a view similar to FIG. 5b showing another modified example of the inner frame of FIG. 5a;

FIG. 6 is a vertical sectional view explanatory of the motion of a lid from its closed to open postion in the embodiment of FIG. 2;

FIG. 7 is a top plan view of another preferred embodiment of the invention designed exclusively for use as a smokeproof screen;

FIG. 8 is an enlarged, partial vertical sectional view of the embodiment of FIG. 7;

FIG. 9 is a vertical sectional view of the embodiment of FIG. 7 taken along a plane 90 turned from the plane of FIG. 8;

FIG. I is an enlarged perspective view showing means for supporting a lid in the embodiment of FIG. 7; and

FIG. I I is a vertical sectional view explanatory of the motion of the lid from its closed to open position in the embodiment of FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first preferred embodiment of this invention will now be described with reference to FIGS. 1 to 6. Referring first to FIG. I, the apparatus according to the invention includes an outer frame I having a rectangular space extending therethrough and which is to be mounted on a ceiling in a manner hereinafter set forth. The outer frame I can be formed of four identical lightweight steel members In, Ih, If and Id rigidly combined together into the hollow, rectangular shape by means of L-shaped reinforcements 2 provided on the inside of the respective corners of the rectangularly combined members and securely affixed thereto by screws 3. If desired, the members In to Id may be welded together at theirjunctions 4 for added strength. Alternatively, the outer frame 1 may be integrally molded as by the technique of die casting.

As best illustrated in FIG. 2 and as also shown in FIG. 3. each of the constituent members In to Id of the outer frame I comprises a hollow, substantially rectangular-sectioned portion 7 including an inner wall 50 and an outer wall h, an upper flange 8 extending horizontally inward from the top of the portion 7. and a lower flange 9 supporting the edge of the ceiling as in the drawings. The aforesaid inner wall 5a is recessed at 6 to define a guide groove extending horizontally throughout the entire length ofeach of the members In to Id, as will be seen more clearly by referring back to FIG. 1.

FIG. 2 best illustrates the means for mounting the outer frame I on the ceiling. A channel-shaped support member 12 is fixedly mounted crosswise on joists II which support the furring strips I0 of the ceiling. A fixture I3 is attached to the outside surface of each of the constituent members In to Id of the outer frame I and is securely coupled to a bolt 14 through a knuckle pin IS. The bolt I4 is fastened to the support member I2 by a pair of thumbscrews I6 so that the outer frame 1 is securely held in position with its lower flange 9 in proper engagement with the edges of the ceiling I7.

The outer frame 1 thus mounted on the ceiling is to serve as an emergency smoke vent by having a duct I8 coupled thereto through its upper flange 8. However, in case a lid normally closing the lower end of the outer frame I is intended for use as a smokeproof screen, as set forth more specifically in the second embodiment of the invention, the open upper end of the outer frame may be closed by a sheet 2| of appropriate material fixedly mounted on the upper flange 8, as indicated by the dot-and-dash lines in FIGS. 2 and 3.

The construction of the lid 20 openably closing the lower end of the outer frame I will be best apparent from FIG. 5. Broadly, the lid 20 is comprised of an inner frame 22 of shape and size substantially corresponding to those of the outer frame I, and a panel 23 supported by the inner frame 22 so as to be flush with the ceiling 17 as shown in FIGS. 2 and 3 and preferably made of the same material as the ceiling I7 to permit the apparatus to be inconspicuously mounted. The

inner frame 22 includes an upper portion 24 composed of four hollow, rectangular-sectioned members 24a, 24b, 24c and 24d of lightweight steel or the like, and a lower portion 25 composed of four substantially U- shaped members 25a, 25b, 25c, and 25d of lightweight steel or the like.

The four constituent members 240 to 24:1 of the upper portion 24 are rigidly secured to each other by L-shaped reinforcements 26 provided on the inside of the respective corners of the rectangularly combined members and screwed or otherwise fastened thereto. The four constituent members 250 to 25d of the lower portion 25 are secured at their upper ends 28 to the outer surfaces of the upper portion 24 by means of screws 30.

However, as seen in FIG. 5a, one of the four constituent members of the lower portion 25 is to be screwed to the upper portion 24 only after the aforesaid panel 23 has been placed on the bent lower ends 29 of the other three members already screwed to the upper portion 24. In this manner the assemblage of the lid 20 is highly facilitated.

It is to be understood that the makeup of the lid 20 set forth in detail hercinbefore is purely by way of example. Only if one (25d in FIG. 5a) of the constituent members 25a to 25d of the lower portion 25 is formed independently of the corresponding member (24d in the same drawing) of the upper portion 24, so as to be screwed or otherwise united together after insertion of the panel 23 into the lower portion 25, then the other members (250 to 25c) of the lower portion 25 can be formed integrally with the respective corresponding members 24a to 240) of the upper portion 24, as illustrated in FIG. 5b.

If desired, blocks 32 of resilient material such for example as rubber can be interposed between the corresponding members of the upper and the lower portions 24 and 25 as in FIG. 50. Thus, by regulating the tightness of screws 33 fastening the lower portion members to the respective upper portion members, the dimensions of the lower portion 25 can be varied for adjustment of the gaps G, FIG. 2, between itself and the outer frame I. The resilient blocks 32 can of course be replaced by washers.

As illustrated in FIGS. 2 to 4, the lid 20 of the above described construction is supported within the outer frame I by a pair of rods 34 along one end thereof. Each of these rods 34 is composed of a smaller diameter portion 35 and a guide portion 36 of larger diameter formed at the outer end of the smaller diameter portion. The smaller diameter portion 35 is both slidably and rotatably received in a sleeve 37 affixed to the said one end of the lid 20, whereas the guide portion 36 is received in the guide groove 6 formed on the corresponding inside wall of the outer frame I. In order to permit the guide portions 36 to slide along the guide groove 6 on the confronting walls of the outer frame without suffering undue friction, it is preferable that the entire guide portions or at least their surfaces be made of a suitable synthetic resin.

It will be noted from FIG. 3 that the rods 34 are urged against the respective guide grooves 6 by helical compression springs 38 housed in the respective sleeves 37. The friction to be exerted between the guide portions 36 and the grooves 6 is regulatable by means of adjusting screws 39.

A pair of arms 40 extend between the two opposite ends of the lid and the respective corresponding inside walls of the outer frame 1. Each of the arms has one of its ends turnably coupled by a pin 42 to a support 41 secured to the inside wall of the outer frame I and the other end turnably coupled by a pin 44 to a support 43 secured approximately centrally of the outside edge of the lid 20.

As seen in FIG. 2, lock means generally designated by the numeral 45 is secured on the inside of the outer frame I to normally hold the lid 20 in the closed position by engaging a latch 46 on the free end of the lid. Although not shown in the drawings, it is assumed that the lock means 45 is electrically connected to a smoke detector of any known construction, so that the latch 46 will be released upon introduction of an actuating signal to the lock means from the smoke detector in accordance with the prior art. Of course, the relative positions of the lock means 45 and the latch 46 can be reversed without departing from the scope of the invention.

Proceeding to the description of a mode of operation of this first preferred embodiment of the invention, constructed substantially as hcreinbefore described,

the lock means 45 becomes operative to release the latch 46 when actuated by the smoke detector. Thereupon the lid 20 starts moving by gravity as shown in FIG. 6, in such a manner that the lid turns downwardly on the rods 34 while being pulled forwardly, or to the left as viewed in FIGS. 2 and 6, by the arms 40 as the guide portions 36 of the rods 34 travel slidingly along the respective guide grooves 6.

As will be understood from FIG. 6, the free end of the lid 20 descends substantially vertically as the lid moves from its closed or horizontal portion to its open or vertical position, and in the open position of the lid 20 the guide portions 36 of the rods 34 are positioned to the extreme left, as seen in FIGS. 2 and 6, of the guide grooves 6. It will not be apparent that since the lid 20 is not turned on a fixed fulcrum, the spacings G, FIG. 2, between the front and rear ends of the lid and the corresponding surfaces of the outer frame 1 can be minimized. Moreover, the impact which may he produced upon descent of the lid 20 can be cushioned by the friction exerted as the guide portions 36 of the rods 34 slide along the respective guide grooves 6. The friction thus exerted is regulatable as aforesaid by the adjusting screws 39 thereby simultaneously controlling the speed of descent of the lid 20.

However, the friction to be exerted between the guide portions 36 and the respective grooves 6 is subject to change with the lapse of time or due to the heat that may be generated in the event of a fire, so that it is possible that the lid 20 be opened without being sufficiently decelerated by the friction only. To obviate this, buffers such for example as helical compression springs 47, FIG. 6, can be installed on the left-hand ends of the respective guide grooves 6 so as to yieldingly contact the guide portions 36 upon descent of the lid 20 and hence to cushion its impact.

As the lid 20 has been moved to its open position in the manner set forth hereinbefore, the smoke filled in the enclosed space under the ceiling 17 may be caused to escape through the duct 18 connected to the outer frame I with the aid of a blower or the like not shown in the drawings. In case the lid 20 itself is intended for use as a smokcproof screen, it is required to have a sufficient length to extend from wall to wall of the room or other enclosed space under the ceiling. FIGS. 7 to II inclusive illustrate another preferred embodiment of the invention which is believed to be more suitable for use for this purpose and in which different means are employed to support a lid which usually will be considerably longer and thus heavier than the lid 20 of the FIGS. I to 6 embodiment.

The reference numerals 47 and 48 in FIG. 7 denote the confronting walls of a room or the like between which the outer frame I is supported by the above described means including the joists ll of the ceiling, the channel-shaped support members l2, the bolts I4 and so forth. The outer frame 1 of this second embodiment is substantially of identical construction with the outer frame of the preceding embodiment, except that it is sufficiently long to span the opposite walls 47 and 48 of the enclosed space. The lid 20 is also correspondingly elongated to lit in the outer frame I with appropriate clearance.

In order firmly to support the elongated lid 20, one or more, two in this embodiment, crossheams 49 extend between the two opposed longer sides of the outer frame I as best shown in FIG. 7. As illustrated in further detail in FIG. 8, each of the crossheams 49 includes a hollow, rectangular-sectioned portion 50, a flange 51 formed on the top of the portion 50. and a pair of guide grooves 52 formed under the portion 50, and is coupled to the opposite inside walls of the outer frame 1 by screws, not shown, which are received in screw pockets 53 formed within the portion 50.

Crossheams 54 of hollow, substantially rectangularsectioned shape are also provided to the lid 20 so as to be positioned on both sides of each of the first mentioned crossheams 49, and each pair of the crossheams 54 are interconnected by a plate member 55 screwed at 56 to the bottoms of the respective cross-beams 54. The rods 34 set forth in connection with the preceding embodiment are provided at one end of the lid 20 as shown in FIG. 8, and their guide portions 36 are received in the respective guide grooves 6 formed in the inside walls of the outer frame I and in the guide grooves 52 formed in the crossheams 49.

However, the rods 34 and the arms 40 of the preceding embodiment must be modified in construction in order to prevent the lid 20 from striking against the crossheams 49 during its descent to the open position. As illustrated in detail in FIG. I0, each rod 34 in this second embodiment is provided in the form of an L- shaped movable member 58 having the guide portion 36 formed on one end thereof. The L-shapcd members 58 are slidably inserted into respective sleeves or guides 59 secured in places to the lid 20 and are prevented from detachment therefrom by stops 60 formed on the other ends thereof.

In addition to the arms 40 extending between the two opposite ends of the lid 20 and the respective corresponding surfaces of the outer frame I as in the preceding embodiment, there are provided additional arms extending between the crossheams 49 and 54 of the outer frame I and the lid 20 respectively, as will be seen from FIG. 8. All these arms are of identical construction, and as best illustrated in FIGS. 9 and 11, the pin 44 on one end of each arm 40 is slidably received in a slot 61 of prescribed length formed in each of the supports 43 secured in places to the lid 20.

The lock means 45 in combination with the latch 46, FIG. 9, can be provided in one or more positions on the outer frame 1 and the lid 20, respectively, normally to hold the lid in the closed position. As in the preceding embodiment, it is assumed that the one or more lock means 45 are electrically connected to the smoke detector of known construction so as to be automatically actuated in event the smoke is detected in the enclosed space under the ceiling. The upper end of the outer frame I is permanently closed by a sheet 62 of any appropriate material.

in the second preferred embodiment of the invention, constructed as shown in FlGS. 7 to II, the lid 20 is caused by gravity to move to its open position as the latch or latches 46 are released from the lock means 45. As set forth in connection with the preceding embodiment, the lid 20 turns downwardly on the guide portions 36 formed at the tips of the respective L- shaped members 58 while being pulled forwardly by the arms 40 as the guide portions 36 travel slidingly along the respective guide grooves 6 and 52., as will be understood from FIG. ll.

Furthermore. since the arms 40 and the L-shaped members 58 are both slidable to a predetermined extent relative to the lid 20. this lid is permitted to descent to its open or vertical position without striking against the crossbcams 49 of the outer frame I as it is displaced downwardly during its travel to the open position.

The lid 20 thus moved to its open position will serve by itself as a smokeproof screen to retard the spread of the smoke throughout the enclosed space. However, since the gaps between the lid 20 and the walls 47 and 48 should be eliminated altogether in order to make still more effective the service of the lid as the smokeproof screen, a pair of stopgap members 64, H68. 8 and ll. of required thickness can be turnably pinned at 63 to the walls 47 and 48 respectively so as neatly to close the gaps left by the lid 20 in its open position.

Although the apparatus according to this invention has been shown and described hcreinbeforc in terms of some preferred embodiments thereof, it is to be clearly understood that all matter described herein or shown in the accompanying drawings is by way of example only and is not restrictive of the invention in any way. It is therefore appropriate that the invention be construed broadly and in a manner consistent with the fair meaning or proper scope of the appended claims.

What is claimed is:

I. An apparatus designed to provide a smoke vent or smokeproof screen, comprising an outer frame fixedly mounted on a ceiling to define a generally rectangular opening therethrough which extends between two opposite walls of an enclosed space under said ceiling,

said outer frame having horizontally extending guide guide grooves of said outer frame and of said cross 6 beam; lock means for normally holding said lid in the closed position; a smoke detector for actuating said lock means; a plurality of turnable arms connecting said lid to said outer frame and to said crossbeam in such a manner that when said lock means is actuated to unlock said lid, the same is caused by gravity to move to the open position while its free end is caused to move substantially vc rtically downward said guide portions of said support means slide along said respective guide grooves of said outer frame and of said crossbeam.

2. The apparatus as defined in claim 1. wherein said lid comprises an inner frame and a panel supported thereby so as to be flush with said ceiling, the spacing between the front and rear ends of said lid and the surfaces of said outer frame being minimized, said panel being made of the same material as said ceiling.

3. An apparatus designed to provide a smoke vent or smokcproof screen comprising an outer frame fixedly mounted on a ceiling to define a generally rectangular opening therethrough which extends between two opposite walls of an enclosed space under said ceiling, said outer frame having horizontally extending guide grooves formed on the confronting inside surfaces thereof; at least one crossbeam provided to said outer frame, said crossbeam also having horizontally extending guide grooves formed on both sides thereof; a lid normally closing said rectangular opening formed through said ceiling; support means openably supporting said lid at one end thereof and including a plurality of guide portions slidably received in said respective guide grooves of said outer frame and of said crossbeam; lock means for normally holding said lid in the closed position; a smoke detector for actuating said lock means; a plurality of turnable arms connecting said lid to said outer frame and to said crossbeam in such a manner that when said lock means is actuated to unlock said lid, the same is caused by gravity to move to the open position while its free end is caused to move substantially vertically downward said guide portions of said support means slide along said respective guide grooves of said outer frame and of said crossbeam, and wherein said support means comprise a plurality of L-shaped members each coupled at one end to said one end of said lid so as to be slidable to a predetermined extent relative to said lid and each having one of said guide portions formed on the other end to be slidably received in each of said guide grooves of said outer frame and of said crossbeam, and wherein each of said arms is also coupled at one end to said lid so as to be slidable relative to said lid, whereby said lid is permitted to move to the open position without striking against said crossbeam.

4. An apparatus designed to provide a smoke vent or smokcproof screen comprising an outer frame fixedly mounted on a ceiling to define a generally rectangular opening therethrough which extends between two opposite walls of an enclosed space under said ceiling, said outer frame having horizontally extending guide grooves formed on the confronting inside surfaces thereof; at least one crossbeam provided to said outer frame, said crossbeam also having horizontally extending guide grooves formed on both sides thereof; a lid normally closing said rectangular opening formed through said ceiling; support means openably supporting said lid at one end thereof and including a plurality of guide portions slidably received in said respective guide grooves of said outer frame and of said crossbeam; lock means for normally holding said lid in the closed position; a smoke detector for actuating said tive guide grooves of said outer frame and of said crossbeam. and including a pair of stopgap members turnahly supported on said respective opposite walls of the enclosed space to close the gaps formed between said lid and said respective walls when said lid is moved to the open position. 

1. An apparatus designed to provide a smoke vent or smokeproof screen, comprising an outer frame fixedly mounted on a ceiling to define a generally rectangular opening therethrough which extends between two opposite walls of an enclosed space under said ceiling, said outer frame having horizontally extending guide grooves formed on the confronting inside surfaces thereof; at least one cross-beam provided to said outer frame, said crossbeam also having horizontally extending guide grooves formed on both sides thereof; a lid normally closing said rectangular opening formed through said ceiling; support means openably supporting said lid at one end thereof and including a plurality of guide portions slidably received in said respective guide grooves of said outer frame and of said crossbeam; lock means for normally holding said lid in the closed position; a smoke detector for actuating said lock means; a plurality of turnable arms connecting said lid to said outer frame and to said crossbeam in such a manner that when said lock means is actuated to unlock said lid, the same is caused by gravity to move to the open position while its free end is caused to move substantially vertically downward as said guide portions of said support means slide along said respective guide grooves of said outer frame and of said crossbeam.
 2. The apparatus as defined in claim 1, wherein said lid comprises an inner frame and a panel supported thereby so as to be flush with said ceiling, the spacing between the front and rear ends of said lid and the surfaces of said outer frame being minimized, said panel being made of the same material as said ceiling.
 3. An apparatus designed to provide a smoke vent or smokeproof screen comprising an outer frame fixedly mounted on a ceiling to define a generally rectangular opening therethrough which extends between two opposite walls of an enclosed space under said ceiling, said outer frame having horizontally extending guide grooves formed on the confronting inside surfaces thereof; at least one crossbeam provided to said outer frame, said crossbeam also having horizontally extending guide grooves formed on both sides thereof; a lid normally closing said rectangular opening formed through said ceiling; support means openably supporting said lid at one end thereof and including a plurality of guide portions slidably received in said respective guide grooves of said outer frame and of said cross-beam; lock means for normally holding said lid in the closed position; a smoke detector for actuating said lock means; a plurality of turnable arms connecting said lid to said outer frame and to said crossbeam in such a manner that when said lock means is actuated to unlock said lid, the same is caused by gravity to move to the open position while its free end is caused to move substantially vertically downward as said guide portions of said support means slide along said respective guide grooves of said outer frame and of said crossbeam, and wherein said support means comprise a plurality of L-shaped members each coupled at one end to said one end of said lid so as to be slidable to a predetermined extent relative to said lid and each having one of said guide portions formed on the other end to be Slidably received in each of said guide grooves of said outer frame and of said crossbeam, and wherein each of said arms is also coupled at one end to said lid so as to be slidable relative to said lid, whereby said lid is permitted to move to the open position without striking against said crossbeam.
 4. An apparatus designed to provide a smoke vent or smokeproof screen comprising an outer frame fixedly mounted on a ceiling to define a generally rectangular opening therethrough which extends between two opposite walls of an enclosed space under said ceiling, said outer frame having horizontally extending guide grooves formed on the confronting inside surfaces thereof; at least one crossbeam provided to said outer frame, said crossbeam also having horizontally extending guide grooves formed on both sides thereof; a lid normally closing said rectangular opening formed through said ceiling; support means openably supporting said lid at one end thereof and including a plurality of guide portions slidably received in said respective guide grooves of said outer frame and of said cross-beam; lock means for normally holding said lid in the closed position; a smoke detector for actuating said lock means; a plurality of turnable arms connecting said lid to said outer frame and to said crossbeam in such a manner that when said lock means is actuated to unlock said lid, the same is caused by gravity to move to the open position while its free end is caused to move substantially vertically downward as said guide portions of said support means slide along said respective guide grooves of said outer frame and of said crossbeam, and including a pair of stopgap members turnably supported on said respective opposite walls of the enclosed space to close the gaps formed between said lid and said respective walls when said lid is moved to the open position. 